Hand-held acoustic camera

ABSTRACT

An acoustic camera includes an acoustic transmitter disposed at one longitudinal end of a housing. The transmitter has a convex radiating surface. A diameter of the transmitter is about four times a wavelength of acoustic energy emitted by the transmitter. A plurality of acoustic receivers is disposed at spaced locations in a pattern extending laterally from the housing. A signal processor is in signal communication with the acoustic receivers. The signal processor is configured to cause the acoustic receivers to be sensitive along steered beams. The signal processor is configured to cause an end of the steered beams to move through a selected pattern within a beam width of the acoustic energy emitted by the acoustic transmitter. The signal processor is configured to operate a visual display device to generate a visual representation corresponding to acoustic energy detected by the acoustic receivers. A visual display device is in signal communication with the signal processor.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of acoustic imaging. Moreparticularly, the invention relates to hand-held acoustic imagingdevices that may be used to visually assess an area in which opticalimaging is obscured.

2. Background Art

Certain emergency situations, such as fires, result in interior spacesof buildings that may have hazards and trapped persons present therein.Rescue personnel may be prevented from readily determining the presenceof such hazards and trapped persons by reason of smoke from the fire.Any optical searching tools, such as lights and cameras are similarlyaffected by smoke, making visual determination of the situation within aburning building difficult to determine.

In fire situations, infrared or other heat sensitive imaging may beimpractical because of the fire itself.

There exists a need for devices that can image the interior of abuilding or other structure through smoke and haze. Such devices arepreferably hand held and readily transportable by its users.

SUMMARY OF THE INVENTION

An acoustic camera includes an acoustic transmitter disposed at onelongitudinal end of a housing. The transmitter has a convex radiatingsurface. A diameter of the transmitter is about four times a wavelengthof acoustic energy emitted by the transmitter. A plurality of acousticreceivers is disposed at spaced positions in a pattern extendinglaterally from the housing. A signal processor is in signalcommunication with the acoustic receivers. The signal processor isconfigured to cause the acoustic receivers to be sensitive along steeredbeams. The signal processor is configured to cause an end of the steeredbeams to move through a selected pattern within a beam width of theacoustic energy emitted by the acoustic transmitter. The signalprocessor is configured to operate a visual display device to generate avisual representation corresponding to acoustic energy detected by theacoustic receivers. A visual display device is in signal communicationwith the signal processor.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an example camera.

FIG. 1A is a cut away side view of the example camera of FIG. 1.

FIG. 2 is an end view of the example camera of FIG. 1 with sensorsdeployed.

FIG. 3 is a graph of sensor output with respect to distance to a targetimage object.

FIG. 4A is an example of signals detected from a human object.

FIG. 4B is an example of signals detected from an inanimate object.

FIGS. 5A and 5B show graphs of a beam pattern of a transmitter for theexample camera.

FIGS. 6A and 6B show graphs of a product of the beam patter of thetransmitter with steered beams of receiver signals

DETAILED DESCRIPTION

An example acoustic camera is shown in side view in FIG. 1, and in cutaway side view in FIG. 1A. Reference herein is made to both figures forpurposes of explaining the example acoustic camera. The camera 10 may bedisposed in a water tight, substantially cylindrical housing 12 such asmay be made from steel, aluminium, plastic or other suitable solidmaterial. The housing 12 may include externally disposed slots 27 orsimilar recesses for deployment arms 24 or similar linkage each biasedby a spring 26 or other biasing device to urge the deployment arms 24longitudinally toward one end of the housing 12. The arms 24 are eachpivotally coupled at their end to a corresponding receiver arm 20. Thereceiver arms 20 are pivotally coupled at one end to the housing 12.Acoustic receivers 22 are disposed on each receiver arm 20. The acousticreceivers 22 will be further explained below. An acoustic transmitter 16may be disposed at the longitudinal end of the housing 12. Thetransmitter 16 may be a piezoelectric element and may be covered, forexample by a number of material layers 17 of thickness explained belowto act as impedance matching devices between the transmitter and asuitably shaped epoxy layer end cap 18. The function of the end cap 18will be further explained below. The housing 12 may include in itsinterior a transmitter driver 28 in signal communication with thetransmitter 16, which causes the transmitter 16 to emit acoustic pulsesof selected frequency and duration. Examples of such pulses will befurther explained below. A receiver processor 30, which may be a digitalsignal processor such as mixed signal application specific integratedcircuit, may be in signal communication with each of the receivers 22and configured to determined steered beams from signals detected by thereceivers 22 in response to acoustic energy from the transmitter 16reflecting from objects in the field of the acoustic output beam of thetransmitter 16. The steered beams for the receiver signals will beexplained further below. A display driver 32 receives signals from thereceiver processor 32 corresponding to signals detected by the receivers22 and preferably processed to generate the steered beams.

The display driver 32 and receiver processor 30 in combination may beconfigured to convert the signals detected by the receivers 22 into atwo dimensional acoustic image, e.g., by display of amplitude ofdetected acoustic signals, for example, in a selectable range window ata selectable range in a corresponding gray scale or color scale withrespect to position of the target as determined by the steered beamproduced by the receiver processor 30 as it interrogates the receivers22. Such two dimensional image may be transmitted from the displaydriver to a visual display device (“display”) 14 such as a liquidcrystal display or plasma display that converts signals from the displaydriver 32 into a visually observable display. The display 14 may also bepivotally coupled to the housing 12 so that it may be movedsubstantially flat against the housing 12 during transport and can bepivotally opened to the position as shown in FIG. 1A for use.

Electrical power to operate the foregoing electronic devices, includingfor example the display 14, the display driver 32, the receiverprocessor 30, the transmitter driver 28 and the transmitter 16 may beprovided by suitable batteries 34 or similar energy storage device. Auser interface 13, which may be, for example, a thumbwheel coupled to apotentiometer, a keypad, or other device that enables the user to inputselected control signals to the display driver 32 and/or the receiverprocessor 30. The user interface 13 may include an audio transducer 15such as small loudspeaker or piezoelectric device that may be used togenerate audible signals, as will be explained in more detail below. Thecontrol signals from the user interface 13 may cause the camera 10 tooperate in different modes, for example and as will be further explainedbelow, to reduce the effective angular range of an image displayed onthe display 14, or, for example, to change the operating mode of thetransmitter 16 and the receivers 22 to enable distinguishing betweentypes of objects detected as a result of acoustic energy from thetransmitter 16 being reflected from such objects. The user interface 13may also be used to select signal detection time, as will be explainedbelow, so that an image generated on the display 14 will correspond to aselected distance or range thereof ob objects imaged by the camera 10.

FIG. 1 shows the camera 10 with the deployment arms (24 in FIG. 1A andreceiver arms (20 in FIG. 1A) in their closed position. When the camera10 is not in use, the foregoing as well as the display 14 may be closedto reduce the size of the camera 10 for convenience. FIG. 1 showsexample dimensions for a version of the camera 10 that can be hand held.A suitable latch (not shown) may hold the deployment arms (24 in FIG.1A) and receiver arms (20 in FIG. 1A) in the position shown in FIG. 1for transport of the camera 10. After use, the respective arms (and thedisplay 14) may be returned to positions such as shown in FIG. 1 fortransportation. FIG. 1 also shows example dimensions for one embodimentof the camera having a transmitter and receivers configured as will befurther explained below. The examiner dimensions are about 60millimeters in diameter and 300 millimeters in length. The foregoingdimensions are intended to make the camera practical to use but are inno way intended to limit the scope of the present invention.

FIG. 2 shows an end view of the camera 10 with the receiver arms 20 inthe deployed position to illustrate an example configuration for thereceivers 22. When the arms 20 are in the deployed position (e.g., asshown in FIG. 1A), the receivers 22 form a selected pattern which in thepresent example is essentially a radial line or “star” pattern disposedin a single plane. In the present example, there can be sixteen receiverarms 20, substantially evenly circumferentially spaced about theexterior of the housing (12 in FIG. 1A) and extending in a directionsubstantially normal to the longitudinal axis thereof, that is,laterally from the centreline of the housing 12. Each receiver arm 20may include, for example, six receivers 22 as shown disposed atsubstantially evenly spaced apart positions along each arm 20.

It should be understood that the manner of mounting the receivers 22 tothe housing in the present example is primarily for convenience. It iswithin the scope of the present invention to mount the receivers 22fixedly or immovably with respect to the housing 12. The receivers 22may be disposed in other patterns than radial or laterally extendinglines.

The physical size of the camera 10 should be practical for a user, e.g.,rescue and safety personnel, to carry, for example, by hand or on a toolbelt or the like. Considerations of the acoustics with respect to apractical size of the camera 10 have led to a design in which thetransmitter (16 in FIG. 1A) can be a relatively small disc at the centerof the longitudinal end of the housing (12 in FIG. 1A) and the receivers(22 in FIGS. 1A and 2) may be small acoustic sensors distributed over anarea as shown in FIG. 2 with a diameter of about 20 to 25 wavelengths(λ=8.6 mm at 40 kHz). In one example, the receivers (22 in FIG. 2) maybe piezoelectric transducers sold under model number E-152/40 by MassaProducts Corporation, 280 Lincoln St., Hingham, Mass. 02043. Theforegoing transducers have a diameter of about 11 millimeters and may bespaced from each other (center to center) on the arms by about 1.5λ(about 13 millimeters at the selected operating frequency of 40 KHz. Thetransmitter 16 may be a piezoelectric transducer such as one sold undermodel number TR-89/B Type 40 by Massa Products Corporation. Theforegoing transducer has a diameter of about 32 millimeters.

The transmitter driver 28 may be configured to cause the transmitter 16to emit acoustic pulses consisting of a selected number of cycles at acenter frequency of about 40 kHz. Typically each pulse includes ten orfewer cycles to provide the required bandwidth so that the camera 10will have a range resolution of a few centimeters and also to providethe bandwidth necessary for the operator to distinguish between variousobjects using an audio presentation feature (explained below). The rangeresolution can be determined by the formula 0.5×sound speed×number ofcycles×period, whererin the period=1/frequency). The acoustic energyfrom the transmitter 16 is reflected from objects within the field ofthe acoustic energy emitted by the transmitter 16. The reflected energymay be detected by the receivers 22. The distance to any particularobject (not shown) from the camera 10 is related to the two way acoustictravel time of the acoustic energy. In the present example, the receiverprocessor 30 may be configured to detect signals from the receivers onlywithin a limited, predetermined time range related to the distance fromthe camera 10. Such time range may be user selectable, e.g., by the useroperating the interface 13. The resulting distance may be shown in thedisplay 14 by suitable programming of the display driver 32. Thus, theuser may view a two dimensional display related to objects disposed at aselected distance, or range of distances, from the camera 10.

It has been determined through acoustic modeling that a number of narrowsteered beams, each subtending an angle of about two degrees anddirectable within an angular range of ±20 degrees from the longitudinalaxis of the camera 10 can be obtained using the radial-line type ofreceiver arrangement as shown in FIG. 2. The radial spacing betweenindividual receivers 22 can be about 1.5λ, or 13 millimeters asexplained above. The angular range over which narrow beams are steeredcan be adjustable down from ±20 degrees from the camera centerline,depending on the range selected and the operator's choice. Such changein angle range of the steered beams may be performed, for example, byreprogramming the receiver processor (30 in FIG. 1A). Such reprogrammingmay be obtained, for example, by the user operating the user interface(13 in FIG. 1A).

A broad, substantially uniform transmitter beam results from atransmitter whose dimensions are small with respect to the wavelength ofthe emitted acoustic energy. However, such a beam would be both toobroad and have too little power for useful imaging. As the transmittersize is increased with respect to wavelength, however, the beam widthreduces and the power output can be increased. Thus, the selected sizeof the transmitter in the present example represents an optimization ofpower output and beam width. Referring once again to FIG. 1A, as amatter of physics, a piston-type transmitter (i.e., a transmitter havinga flat radiating surface) having a diameter of 4λ provides a full beamwidth of about 15 degrees. This is believed to be insufficient forpurposes of acoustic imaging in the intended uses for the present camera10. In the present invention, therefore, the transmitter 16 can becovered by a spherical cap, e.g. epoxy layer 18 on the so that theeffective radiating area can be larger than that of a 4λ diameterpiston. The end cap 18 (or as explained above, a similarly shapedtransducer) enables a desired transmitter beam width of about twentydegrees in either direction from the centerline of the camera 10 (fortydegrees total subtended angle). Typically, the example transmittertransducer described above is a substantially flat disk. In the presentexample, the layers of material 17 each being about λ/4 in thickness canbe applied to the radiating surface of the transmitter 16 to serve asimpedance transformers. A final layer of epoxy or similar material canbe made into a convex surface, e.g., in a truncated, substantiallyhemispherical shape as shown at 18 (the end cap) in FIG. 1A so that aneffective spherical cap radiator is formed. The effective beam width ofa spherical cap is determined by its radius of curvature, and in thepresent example, the radius (example below) may be selected to providean effective transmitter beam width of about 20 degrees, that is twentydegrees in any direction from the centreline of the transmitter 16.Alternatively, the active element of the transmitter 16, which may be apiezoelectric material, itself can be formed into a similar convex shapeon manufacture. Such configuration of the transmitter would eliminatethe need for the impedance matching layers 17 and the end cap 18. Theselected transmitter beam width is believed to provide sufficientillumination area for useful imaging, while retaining sufficienttransmitted power within the beam for useful imaging.

FIGS. 5A and 5B show three and two dimensional graphs, respectively, ofthe beam pattern for the transmitter (16 in FIG. 1A) configured asexplained above. Such pattern is formed using the spherical end cap (18in FIG. 1A) of epoxy on the radiating surface of the transmitter (16 inFIG. 1A). The end cap (18 in FIG. 1A) as explained above has a diameterof about 4λ (32 millimeters) at 40 KHz. The thickness of the end cap (18in FIG. 1A) at the radial center thereof is about 0.576λ. Thetransmitter beam pattern is substantially independent of distance fromthe transmitter (16 in FIG. 1).

An image may be generated by forming a number of narrow beams (e.g., byapplying suitable time delay to the signals detected by each of thereceivers to cause effective beam steering) in the reception of acousticechoes by the receivers (22 in FIG. 2). The beams may be scannedelectronically by the receiver processor (30 in FIG. 1A) across the areaenergized by the transmitter (16 in FIG. 1A) and range (time) gated andsent to the display driver (32 in FIG. 1A) for communication to thedisplay (14 in FIG. 1). The exact scanning pattern is a matter ofdiscretion for the system designer and is not intended to limit thescope of the invention. Also, as previously explained, the effectivearea (subtended angle) imaged by the beam steering may be useradjustable. A computer program, which may operate on the receiverprocessor (30 in FIG. 1) may provide all the steered beams (i.e., timedelays) to be pre-programmed, so that for each transmitter output pulse,an entire image of the area energized by the transmitter (16 in FIG. 1)is sent to the display (14 in FIG. 1).

FIGS. 6A and 6B, show, respectively, the amplitude distribution of oneof the receiver steered beams, which is the product of the transmitterbeam (e.g., FIGS. 5A and 5B) with the steered beams directed at an angleof twenty degrees from the centreline of the camera (10 in FIG. 1). Itcan be observed that in the direction of the steered beam, the resultingsignal is substantially focused on the point of the particular steeredbeam, with relatively low signal detection from any other direction.Thus, the signal to noise ratio of the steered beam may be sufficient togenerate usable images for transmission to the display (14 in FIG. 1).

FIG. 3 shows graphs of expected receiver signal amplitude with respectto the transmitter signal amplitude for various values of temperatureand humidity that may be expected, for example, in the interior of aburning building. What may be observed in FIG. 3 is that under the worstexpected acoustic conditions, sufficient signal should be detected bythe receivers to provide usable images (wherein the signal to noiseratio is 10 dB or greater) at a range of not less than about 8 meters.

Referring once again to FIG. 1A, in using the camera, the transmittedsignal illuminates the scene over the beam width of the transmitter 16.Upon detection of the reflected acoustic energy by the receivers 22, thescene may be imaged as the intensity in each of many pre-formed beams ofwidth about 2 degrees. The total signal detection time will extendeffectively for a time consistent with the two way travel time to arange of about 10 meters. The display 14 may show, for example, anamplitude representation of the detected signal present in a selectedrange gate, for example, 0.5 meters. This range gate can be moved in orout by the user operating the interface 13 as explained above. If anobject of interest is observed by the user, the user may desire tolisten to an audible version of the reflected signal. This may beperformed, for example, by the user directing the camera so that theobject is imaged approximately in the center of the display 14. Thetransmitter driver 28, receiver processor 30 and display driver 32 maybe configured to enable the user to select an operating mode wherein thetransmitter 16 emits an acoustic pulse, and the waveform of the receiversignals is communicated to the display 14. A typical response ispresented in FIGS. 4A and 4B, where acoustic pulses are generated at 40kHz and typical echoes from two objects are exhibited.

The first type of object may be an extended object which generates lotsof reflected signals without any really obvious highlights, i.e., it hasfew corners or sharp edges to reflect acoustic energy distinctly. Suchobject could be, for example, an upholstered sofa or a human body. Agraph of detected signal response from such a type of object is shown inFIG. 4A. The other type of object is one which produces reflectedsignals from specific portions thereof, i.e., it has highlights. A graphof detected signal response from such an object is shown in FIG. 4B.Such an object could be an artifact like a chair or desk, or an oildrum, for example. The present explanation is to demonstrate type ofaudio representations from different objects that may be distinguishableby the human ear.

The foregoing object discrimination has been simulated as follows. Asimulated Hann shaded transmitter output signal at 40 kHz is transmittedwith a duration determined by a predetermined bandwidth, for exampleabout 3 KHz. The ability of the target to scatter the incident signalback into the direction of incidence may be characterized by a series ofimpulses. The transmitted signal is convolved with the series ofimpulses to produce an expected receiver signal. The duration of thesequence of impulses is determined by the range (time) gate. The actualduration of the reflected signals from a range gate of about 1 meter isabout 3 milliseconds. If such signal is presented as audio at 8 KHz,being a reduction in frequency by a factor of 5, for example, the 3milliseconds becomes 15 msecs.

In the present example, the echo from the object is detected. It may beconverted in the receiver processor (30 in FIG. 1A) into a series ofsamples at time intervals suitable for digitally representing the 40 kHzsignal. As an example, the processor (30 in FIG. 1A) may sample thereceiver signals every microsecond, corresponding to a samplingfrequency of 1 MHz. This signal is then passed through software, whichmay be implemented in the receiver processor (30 in FIG. 1A) tore-sample the digital samples at a different rate, as for example, 5,microseconds. The re-sampled signal may be within the audio frequencyrange (e.g., up to about 20 KHz) and communicated to the transducer (15in FIG. 1A) in the user interface (13 in FIG. 1A). The echo signal willthus be audible to the user in this example as a signal centered at 5times lower frequency than the original acoustic pulse, which is 8 kHz.

A single occurrence of such an audio signal (15 msec) is not sufficientfor any determinable human reaction. To overcome such limitation theuser may keep the camera directed at the object for a couple of seconds,for example, wherein the acoustic pulsing, detection and communication.By causing repeated echo detection and re-sampling, the audible signalemitted by the transducer (15 in FIG. 1A) may be heard by the user as aneffectively continuous sound. It is expected that the user will be ableto audibly discriminate between the first type of object and the secondtype of object from the audible signals. Simulations have confirmed theforegoing expectation.

An acoustic camera according to the various aspects of the invention mayenable user location of objects where visual or thermal detection is notpossible. In some examples, an audible signal may enable the user todiscriminate the type of object detected by the camera.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. An acoustic camera, comprising: an acoustic transmitter disposed atone longitudinal end of a housing, the transmitter having a convexradiating surface, wherein a diameter of the transmitter is about fourtimes a wavelength of acoustic energy emitted by the transmitter; aplurality of acoustic receivers disposed at spaced apart locations in aselected pattern extending laterally from the housing; a signalprocessor in signal communication with the acoustic receivers, thesignal processor configured to cause the acoustic receivers to besensitive along steered beams; the signal processor configured to causean end of the steered beams to move through a selected pattern within abeam width of the acoustic energy emitted by the acoustic transmitter,the signal processor configured to operate a visual display device togenerate a visual representation corresponding to acoustic energydetected by the acoustic receivers; and a visual display device insignal communication with the signal processor.
 2. The camera of claim 1wherein the signal processor is configured to read amplitude of thesteered beams.
 3. The camera of claim 2 wherein the signal processor isconfigured to read amplitude of the steered beams within a selectabletime range.
 4. The camera of claim 1 wherein a radius of curvature ofthe convex radiating surface is selected to provide a beam width of theemitted acoustic energy of about twenty degrees in each direction from acenterline of the acoustic transmitter.
 5. The camera of claim 1 whereinthe steered beams have a width of about two degrees.
 6. The camera ofclaim 1 wherein the selected receiver pattern comprises lines extendinglaterally from a centerline of the housing.
 7. The camera of claim 6wherein each line is disposed on an arm coupled to the housing.
 8. Thecamera of claim 7 wherein each line comprises at least six of theacoustic receivers, each of the acoustic receivers on each arm spacedapart from an adjacent one of the acoustic receivers by about 1.5 timesa wavelength of the emitted acoustic energy.
 9. The camera of claim 1wherein the wavelength is about 8.6 millimeters.
 10. The camera of claim1 wherein the signal processor is configured to resample signalsdetected by the acoustic receivers to generate an audio frequency rangesignal, and wherein the camera comprises a transducer in signalcommunication with the signal processor configured to generate anaudible output of the audio frequency range signal.
 11. The camera ofclaim 1 wherein the arms are configured to pivot with respect to thehousing between an open position and closed position substantially flatagainst the housing.
 12. The camera of claim 1 wherein the convexradiating surface comprises epoxy disposed on a flat acoustic transducerelement.
 13. The camera of claim 12 further comprising at least oneimpedance matching layer disposed between the transducer element and theepoxy, the at least one impedance matching layer having a thickness ofabout one-quarter wavelength of the emitted acoustic energy.